Steam reforming is a chemical process in which a hydrocarbon is reacted with steam (H2O) to form hydrogen (H2), CO and CO2. For decades, steam reforming has been the principal industrial process for making hydrogen. More recently, steam reforming has attracted great interest as a possible means to supply hydrogen for fuel cells. There have been intensive research efforts over many years to improve the steam reforming process. Despite these efforts, problems continue to exist with catalyst performance and/or cost, and the need for catalyst replacement or regeneration due to the rather harsh conditions (high temperature and steam) in which steam reforming is typically conducted.
Known steam reforming catalyst support materials include gamma alumina doped with a stabilizing element such as magnesium, lanthanum, and barium. Incorporation of a stabilizer could delay the irreversible transformation of gamma alumina into alpha alumina. However, under severe steam reforming conditions the supports continually sinter, resulting in a permanent loss of active sites.
The effect of rare earth elements and alkaline earth elements as dopants for alumina has been investigated. See Church et al., Appl., Catal., A, 101 (1993) 105. Wachowski, et al., Mater. Chem. and Phys., 37 (1994) 29. Some studies have indicated that there is a correlation between final surface area of alumina treated at high temperatures (1200° C.) and ionic radius of the dopant. Mizukami et al., in A. Cruca (Ed.), Studies in surface science and catalysis, Vol 71, Elsevier Amsterdam, 1991, 557, reported that La3+ and Ba2+ are the most effective dopants among rare earths and alkaline earths, which are large ions with high ionic charges. Yeung et al., J Membrane Sci., 131 (1997) 9, described procedures for making mesoporous alumina membranes by slip casting a 1 M alumina sol (6 wt %) containing 3 atom % of a nitrate of Y, Ba, La, and Ce. Das et al. in Appl. Catal. A: 207, 95-102 (2001), reported that a more stable La-doped support could be obtained by processing in ethanol rather than water. Martin et al. in Appl. Catal. A: 131, 297-307 (1995) described experiments in which Rh was sintered on alumina under H2 at temperatures of 700 to 900° C.; under these conditions, the mean Rh particle size varied from 1.1 to 2.1 nm. Temperature Programmed Reduction (TPR) data was also reported. Schaper et al., in Sintering—Theory and Practice, Proceedings of the 5th International Round Table Conference on Sintering, Material Science Monographs, vol. 14, pp173-176, reported on the influence of Mg, Cr, La and Zr on the stability of gamma alumina catalyst supports and concluded that only lanthanum resulted in a significant improvement in stability against sintering.
Treatment in 10% flowing H2O has been used to pre-age a support for a catalytic convertor. McCabe et al. in J. Catal. 151, 385-393 (1995), reported that presteaming alumina at 1223 K with 10% H2O in flowing air for 24 hours prior to Rh impregnation eliminated irreversible occlusion of Rh during subsequent hydrothermal aging.
Wang et al. in US published patent application 2003/00317105 described methods and catalysts for steam reforming. In one preferred embodiment, the catalyst includes Rh on a Mg—Al spinel. This reference does not describe pretreatment of the support at elevated steam pressure.
Despite extensive efforts over many years, there remains a need for catalytic systems and steam reforming methods that have high performance and stability under the hydrothermal conditions that are typical of steam reforming. Also, despite extensive efforts, there remains a need for better methods of making steam reforming catalysts.